Bruce being an aged, decrepit shithead in Beyond was intended to serve an ultimate goal. One of which was to contrast Terry, who, like TAS Batman, often had a weak spot for his adversaries. Sometimes naively, but generally out of warranted compassion and with levity. Bruce aged into being an asshole looking to punch some motherfuckers and that didn't trust the system/anyone else, but Beyond/Return of the Joker makes it pretty clear that he didn't necessarily start out that way and it certainly didn't glorify that version of Bruce.
Bruce becoming a (warranted) bitter shit also served as a warning for Terry, especially when they wrap up his storyline in DCAU. He had to learn how to balance the responsibilities of the cowl with his social life and not push others away, something that Bruce never managed to figure out and ultimately consumed him.
Even Justice League Unlimited Batman, which is arguably "prime" Batman and Timm and co's darkest, most brooding and most indifferent take within the DCAU, effectively saves the world because he
chooses to empathize with a little girl who's childhood got done raw. Not as the Batman that knocks peoples lights out, but as the bare Bruce Wayne who had his mind read and had to treat someone at their death knell with an ounce of love.